btrfs-progs: add ETA display for device replace operations

Add estimated time of arrival (ETA) calculation for device replace operations
using progress percentage and elapsed time. The ETA is calculated by determining
the total estimated completion time based on current progress ratio and displays
the expected completion time in a user-friendly format.

Author: DocMAX

cmds/replace.c

@@ -46,6 +46,8 @@ static char *progress2string(char *buf, size_t s, int progress_1000);
 
 /* Used to separate internal errors from actual dev replace ioctl results. */
 #define BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_RESULT		-1
+/* Buffer size for ETA string display */
+#define ETA_STR_SIZE						80
 
 static const char *replace_dev_result2string(__u64 result)
 {
@@ -371,6 +373,7 @@ static DEFINE_SIMPLE_COMMAND(replace_start, "start");
 static const char *const cmd_replace_status_usage[] = {
 	"btrfs replace status [-1] <mount_point>",
 	"Print status and progress information of a running device replace operation",
+	"Shows current progress percentage and estimated time of arrival (ETA) for completion.",
 	"",
 	OPTLINE("-1", "print once instead of print continuously until the replace operation finishes (or is canceled)"),
 	NULL
@@ -421,6 +424,8 @@ static int print_replace_status(int fd, const char *path, int once)
 	char string1[80];
 	char string2[80];
 	char string3[80];
+	char eta_str[ETA_STR_SIZE];
+	struct tm eta_tm_buf;
 
 	for (;;) {
 		args.cmd = BTRFS_IOCTL_DEV_REPLACE_CMD_STATUS;
@@ -454,6 +459,27 @@ static int print_replace_status(int fd, const char *path, int once)
 				       progress2string(string3,
 						       sizeof(string3),
 						       status->progress_1000));
+			/* Calculate and display ETA if progress is available */
+			if (status->progress_1000 > 0 && status->time_started > 0) {
+				time_t current_time = time(NULL);
+				time_t elapsed_time = current_time - status->time_started;
+				time_t total_time, remaining_time, eta_time;
+
+				/* Avoid division by zero */
+				if (elapsed_time > 0) {
+					total_time = (elapsed_time * 1000) / status->progress_1000;
+					remaining_time = total_time - elapsed_time;
+
+					/* Only show ETA if we have a reasonable estimate */
+					if (remaining_time > 0 && total_time > elapsed_time) {
+						eta_time = current_time + remaining_time;
+						struct tm *eta_tm = localtime_r(&eta_time, &eta_tm_buf);
+						if (strftime(eta_str, sizeof(eta_str), "ETA: %a %b %d %H:%M:%S %Y", eta_tm) > 0) {
+							num_chars += printf(", %s", eta_str);
+						}
+					}
+				}
+			}
 			break;
 		case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
 			prevent_loop = 1;